POLYETYLENE - DISCOVERY AND HISTORY

Polyethylene was first synthesised by the German chemist Hans von Pechmann, who prepared it by accident in 1898 while heating diazomethane.
When his colleagues Eugen Bamberger and Friedrich Tschirner analysed the white, waxy substance he had created, they recognised that it contained long -CH2- chains and termed it polymethylene.

The first industrially practical polyethylene synthesis was discovered (again by accident) by Eric Fawcett and Reginald Gibson at ICI Chemicals in 1933.
Polyethylene formed upon applying extremely high pressure of several hundred atmospheres to a container with a mixture of ethylene and benzaldehyde. They again produced a similar white waxy material on the sides of the container.

Since the reaction had been initiated by trace oxygen contamination in their apparatus, the experiment was at first difficult to reproduce. It was not until 1935 that another ICI chemist, Michael Perrin, developed a reproducible industrial synthesis for low density polyethylene (LDPE).





The first ton of material showed it had unbeatable electrical isolating qualities and in August 1939 its industrial production began, which was entirely used for the purposes of war (in particular in techniques linked to radar).

Once the war ended, polyethylene risked disappearing from ICI products, but research results on new applications showed that polyethylene was more versatile than originally thought.

Subsequent landmarks in polyethylene synthesis have centred on the development of several types of catalysts that promote ethylene polymerisation at milder temperatures and pressures.
The first of these was a chromium trioxide based catalyst discovered in 1951 by Robert Banks and John Hogan at Phillips Petroleum.

In 1953, the German chemist Karl Ziegler developed a catalytic system based on titanium halides and organoaluminium compounds that worked at even milder conditions than the Phillips catalyst. The latter was less expensive and easier to work with, however both methods are used in the industrial practice of producing HDPE.





Phillips initially had difficulties producing a HDPE product of uniform quality and filled warehouses with off-specification plastic. However, financial ruin was unexpectedly averted in 1957, when the hula hoop, a toy consisting of a circular polyethylene tube, became a fad among teenagers throughout the United States.

A third type of catalytic system, one based on metallocenes, was discovered in 1976 in Germany by Walter Kaminsky and Hansjörg Sinn.
The Ziegler and metallocene catalyst families have since proven to be very flexible at copolymerising ethylene with other olefins and have become the basis for the wide range of polyethylene resins available today.

Some of these resins, in the form of fibres like Dyneema, have begun to replace materials such as Kevlar for applications requiring excellent mechanical resistance to traction.